As is known in the art, RF power amplifiers using depletion mode transistors to amplify an input radio frequency signal often use solid state “drain” switches to turn on and off DC supply power.
An alternative to the drain switch is the gate switch, where a sufficiently negative voltage is supplied to the power amplifier's transistor gate to reduce the DC quiescent current to zero and also provide sufficient isolation in the RF path. An advantage of the gate switch approach is faster switching times between RF enable and off for systems using RF amplifiers. One such circuit (FIG. 1) is shown in U.S. Pat. No. 6,600,301 B1, issued Jul. 29, 2003, inventor DeFalco, assigned to the same assignee as the present invention. While such circuit has been found to be effective in many applications, in applications having a wide variation in temperature and power supply, a sufficient off-state voltage must be applied to it to establish proper quiescent bias for proper RF amplifier operation inclusive of process, temperature, and power supply variations.
As is also known in the art, wide bandgap transistors such as Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT) and Silicon Carbide (SiC) Metal-Semiconductor Field Effect Transistor (MESFET) are great Radio Frequency (RF) power devices for their high voltage swings, high break voltages as well as the excellent thermal conductivity. Si Complimentary Silicon Oxide Semiconductor (CMOS) technologies offer tremendous levels of complexity and integration. Heterogeneous integration of both technologies can enable more features and capabilities of high performance microwave and mmWave systems. However, wide bandgap transistors operate in the range of tens (10s) to hundreds (100s) volts, and the supply voltage of sub-micron Si CMOS circuit is normally under 2.5V. Providing a low voltage CMOS bias control circuits to a high voltage GaN transistor is a challenge. Previously, the attempt had been made to control GaN HEMT bias with Si pMOS, which is operated in high voltage supply, 14 Volts as described in a paper by Kazior, T. E.; Chelakara, R.; Hoke, W.; Bettencourt, J.; Palacios, T.; Lee, H. S. entitled “High Performance Mixed Signal and RF Circuits Enabled by the Direct Monolithic Heterogeneous Integration of GaN HEMTs and Si CMOS on a Silicon Substrate”, Compound Semiconductor Integrated Circuit Symposium (CSICS), 2011 IEEE DOI: 10.1109/CSICS.2011.6062443, Page(s): 1-4.